Project Summary/Abstract There is a lack of well-defined studies regarding the health effects of non-asbestiform elongated mineral particles (EMPs), and a lack of agreement on the appropriate threshold dimensions of EMPs that are health- relevant. The NIOSH Roadmap for Research relating to asbestos fibers and other EMPs (2011) identifies the taconite miners of northeastern Minnesota as a population that should be studied further with detailed exposure characterization. We aim to address the question of health effects of non-asbestiform EMPs, and also the various hypotheses regarding the appropriate dimensions of the EMPs that may be relevant to respiratory health. A previous study has collected large number of personal filter samples that have been analyzed for EMPs using NIOSH 7400/7402. All these personal samples obtained have also been archived for future use. We first propose to re-analyze these samples using ISO TEM 13794 that will provide detailed information on dimension, mineralogy, and habit, and obtain estimates of personal exposures using different dimension-based exposure metrics. Second, we will develop and validate similarly exposed groups (SEGs) based on these exposure metrics. Third, we will obtain relationships (conversion factors) between the different exposure metrics for each SEG, and apply these conversion factors to the historical data to obtain exposure histories of each SEG according to these exposure metrics. Fourth, we will use the estimated exposure histories and employment histories of each worker in the cohort to calculate their cumulative exposures according to each exposure metric. Fifth, we will estimate the risk of mesothelioma, lung cancer and prevalent non-malignant respiratory disease associated with those exposures, both by themselves and in the presence of respirable dust and silica exposures. For this purpose, a large cohort of workers has been assembled with health outcome data with increasing levels of specificity- mortality, incidence of lung cancer, indicators of respiratory morbidity - spirometry, chest X-rays, etc. that have already been collected. This information along with the exposure measurements will be used to address the question of health effects of non-asbestiform EMPs, and also the various hypotheses regarding the appropriate dimensions of the EMPs that may be relevant to respiratory health